PD degradation analysis of PET with enclosed voids and voids connected to closed and vented channels

Polymeric insulating materials with excellent electrical properties are widely used in electrical power equipment. They are degraded however when they are subjected to partial discharges (PD). Factors which control the PD activity include pressure and type of gas present. The pressure variation in a self-contained void will differ from that in voids with channels; also a void with a channel connected to external atmosphere can have the gaseous environment refreshed. A series of experiments is carried out on artificial voids, created from layered sections of polymer. One set of samples has a void inside the polymer with no access to the outer atmosphere; a second set of samples has a void with a closed end channel and a third set of samples has a vent connecting the void to the outer atmosphere. All three sample sets are stressed using the same electrical conditions for the same period of time. Measured differences in PD characteristics and PD induced degradation for the three different arrangements are presented.